One embodiment relates to a composite comprising a ceramic multilayer body, comprising a cermet feedthrough; to a process for manufacturing a composite, comprising a cermet feedthrough; to a composite obtainable by said process; to a device comprising a composite according to one embodiment; and to a use of a plurality of ceramic green sheets and a composition to produce a composite according to one embodiment.
The prior art knows numerous implantable electrical medical devices, for example pacemakers and defibrillators. Pacemakers known in the prior art include a bladder pacemaker, a breath pacemaker, an intestinal pacemaker, a diaphragm pacemaker, a cerebral pacemaker and a cardiac pacemaker. Such devices commonly include a housing enclosing electronics. An electrical source of energy, for example, a battery, may be included by the housing as well or it may be included by a further housing and be connected to the electronics via electrical connectors. The housing which is to be implanted into a human or animal body must hermetically seal the electronics from the surrounding body, that is, it must be leak tight for body fluids and gases. Commonly an object of an implantable electrical medical device involves electrically stimulating tissue, that is, muscles or brain cells, via electrodes or measuring electrical signals of the body via antennae, or both. Therefore, the implantable electrical medical device has to include an electrical feedthrough which electrically connects the inside of the housing to the outside. Such a feedthrough has to be designed to maintain the housing hermetically tight and thus the device implantable. Therefore, an electrical feedthrough for implantable medical devices commonly known in the prior art includes an electrically conductive feedthrough element, here a metal feedthrough wire, which is enclosed by a ceramic ring. Therein, the feedthrough wire is soldered to the ceramic ring via a gold solder. The ceramic ring in turn is soldered into a metal flange, which can be welded to a metal housing. Said feedthrough assembly of the prior art includes several intermaterial connections which may be prone to breaking or leaking. In addition, establishing such intermaterial connections is costly or makes a production process more complicated or lengthy. An improved feedthrough is disclosed in EP 1 897 588 B1. Therein, the metal feedthrough wire is connected to a surrounding ceramic body by means of sintering. This way the number of intermaterial connections and the amount of gold solder used are reduced. The connection between the electrically conductive feedthrough element and the ceramic body could be improved by means of the disclosure of DE 10 2009 035 972 A1. Therein, a feedthrough element made of a cermet is used instead of a metal feedthrough element.
In order to tailor a ceramic body of a desired thickness or quality or both the ceramic body can include multiple ceramic layers. The feedthrough element then electrically connects through the ceramic layers of the ceramic body. Such a multilayer feedthrough may be prepared by stacking and laminating ceramic green sheet tapes, providing holes which connect through the laminate of the green sheet tapes, filling a cermet into the holes and sintering the green sheet tapes and the cermet together by firing at a peak temperature above 1400° C. Therein, the material of the ceramic green sheet tapes and the cermet have to be chosen to have very similar characteristics of their coefficients of thermal expansion (CTE) and sintering. Any mismatch in CTE and/or sintering characteristics of the materials may result in a mechanical stress between the parts upon firing. Said stress may lead to a delamination of the ceramic layers in the surroundings of the cermet or even to a structural damage of the ceramic body.
Therefore, the cermet feedthroughs in ceramic multilayer bodies known in the prior art include at least the following disadvantages. Only small mismatches of CTE or sintering characteristics or both of ceramic materials and cermet materials used for cermet feedthroughs in ceramic multilayer bodies of the prior art are tolerable. The choice of ceramic or cermet or both materials which can be applied for cermet feedthroughs in ceramic multilayer bodies of the prior art are undesirably limited. The choice of combinations of ceramic and cermet materials which can be applied for cermet feedthroughs in ceramic multilayer bodies of the prior art are undesirably limited. Upon producing cermet feedthroughs in ceramic multilayer bodies of the prior art an undesirably high fraction of defect or substandard or both feedthroughs are obtained. An undesirably high effort has to be put into the sintering step of producing cermet feedthroughs in ceramic multilayer bodies of the prior art. Producing cermet feedthroughs in ceramic multilayer bodies of the prior art is undesirably complicated. Producing cermet feedthroughs in ceramic multilayer bodies of the prior art is undesirably expensive.
For these and other reasons, a need exists for the present embodiments.